Effects of doping concentrations on the photocurrent and dark current of a CMOS photodiode

摘要

In this paper we present, for a CMOS n-diffusion photodiode, the effects of various doping concentrations on the behaviour of two of the main parameters that characterize the performance of these devices: the photocurrent (for low and for high levels of the illumination) and the dark current. We performed simulations aided by T-CAD tools for each type of layer of the CMOS photodiode structure (substrate, p-epitaxial layer, n-diffusion layer) and evaluated the behaviour of the photocurrent and dark current in various levels of the doping concentrations of these layers. These results may be helpful in the process of fabricating these devices, where controlled amounts of impurities may be added to some layers (or their level might be reduced in some other layers), in order to maximize the photocurrent and to minimize the dark current in these structures.